Method of making sealing glasses



sept. 19, 1950 R. v. LUKES 2,522,524

METHOD 0F MAKING SEALING GLASSES Original Filed June 24, 1946` (DRY/N6 orf/v l (Ittomeg Patented Sept. 19, 1950 METHOD F MAKING SEALING GLASSES Robert V. iukes, jCorning", N. Y., Qassign'or to Corning Glass Works, Corning, N. Y., a vcorporation of New York original application 11111524, 1946, serial No. g678,l'65,-1 Divided and this application September 19, 1949, Serial N o. 119,327

V1.1 claims. (o1. 21o-:979)

This invention relates to glasses 'which are suitable for forming thermal seals between fused silica or high silica glasses and metals or between fused silica or high silica glasses and other glasses of higher thermal expansion coefli'cients. This application is a division of my pending application Serial Number 678,765, filed June 24, 1946.

The primary object of this invention is to provide glasses having thermal expansion coeiiicints intermediate those of fused silica and ordinary silicate glasses.

. Another object is to provide graded glass seals.

Another object is to provide glass articles having graded expansion coeicients ranging from about .0000008 to .0000020 cm. per cm. per de'- gree C. and higher between 0 and 300 C.

Another object is to provide graded glass seals which are mechanically strengthened by surface compressional stresses. Another object is to provide a simple and easy method of making such glasses and graded seals. In the Patent 2,336,227issued December '7, 1943, to Robert I-I. Dalton and assigned to the assignee of this application, a method of making sealing glasses is described which comprises impregnating a porous high silica glass with a solution or solutions containing glass making materials, which on ring are converted to colorless glass'- forming oxides other than silica, su'chas, voxides of boron, alkali metals, alkaline earth metals, etc., and thereafter ring the impregnated glass 4to close the vpores and incorporate such oxides into the glass as a part of its composition, whereby the thermal expansion coefficient of the high silica glass is increased and its softening point is modified 'to a desired extent. The porous high silica glass is prepared by a well known process described in Patent 2,106,744, issued February 1, '1938, to Harrison P. Hood and Martin E. Nordberg, and comprising leaching non-siliceous con'- ls'tituents from a glass to leave a porous highly siliceous glass having,intercommunicating pores throughout and a silica content of at least v94%. Before firing the impregnated glass it is necessary to dry it, during which time the soluble salts within the pores have a tendency to creep or Ato become more concentrated in the outer portion of the glass thereby establishing differential -stresses between the outer and inner portions of the article when it is subsequently fired. Such differential. stresses comprise a tensional stress at the surface with a corresponding compressional stress in'the interior of vthe glass, which condition promotes breakage. y I

"^I-ha've-now found that this difcult'y may-be aveiuedlby impregnaung the porous glass as above ydescribed and thereafter removing at least a part `article is dried and red to close the pores and incorporate the impregnating materials into the glass Without the development of objectionable stresses'. In fact, the stress condition is reversed and a small 'oomp're'ssional stress is developed in the surface of the glass, which improves its mechanical strength. n 'More specifically, the 'new process comprises immersing at least apart 'of the article in a solution containing a suitable glass making material until the 'pores are lled with the solution ymmersing the impregnated part in a solvent for such glassmaking material, preferably a hot dilute solution of an acid, for about 1 to 2 minutes per mm. of glass thickness, drying the article 'and viiring it to close the pores and incorporate ,the material into the glass. The incorporation of such materials into the glass increases its thermal expansion coeiilcient.

vGlass making materials which are suitable for my purpose are soluble materials or salts which may be combined with silica to form glass, such as boric acid, borax and alkali metal borates, the carbonates and nitrates of the alkali metals, etc. For `some purposes glass coloring materials such as salts of, cobalt, nickel, chromium, etc.,v may be included. Chlorides and acetates are not entirely suitable. Chlorides may not be entirely converted to the corresponding metal oxides and .residual chloride in the glass may cause objectionable vbubbling when the .glass is subsequently :flame worked. vAcetate's may leave a slight carbonaceous residue in the glass which may result in bubbling when the 2glass is flame worked.

Water is preferable as the solvent, but other sol-v vents may `be employed if desired. It is advantageous touse 'a weakly basic solution when bcric 'acid or alkaliJmetal borates are present because vtheir solubilityis thereby substantially increased. 'Ammoniacal solutions are suitable. 'Such solutions readily lose ammonia, particularly when maintained near Ytheir boiling points and it is 'preferable to use ythem in covered containers. 'Ammonia or "solvent which is lost by evaporation may bereplenished either by reiiux or by periodic additions thereof. If 'the cover lits closely and is weighted or otherwise sealed, the heated solution maydevelop a pressure which is somewhat 'above atmospheric pressure. Ammoniacal or alkaline solutions 'may'have a corrosive effect on fthe porous glass and lI have found that such'corrosive effect may be practically nulliied by substantially saturating the solution with silica. This may be done by adding a small amount of a soluble form of silica such as sodium silicate or porous glass cullet or silica gel. A slight turbidity of occulent silica in solution indicates saturation. A larger excess of silica does no harm but is of no advantage.

For the subsequent removal of the soluble materials from the surface or outerportion of the 'glass prior to drying it, the impregnated portion is immersed in a suitable solvent for suchmaterials such as water which is preferably `acidified with a strong acid, particularly When the impregnating solution is alkaline, such as hydrochloric acid, nitric acid, sulfuric acid, etc. A 1% solution of acid is suitable, but stronger or weakerl solutions may also be used. The length of time of immersion will depend upon the temperature of the solution, which preferably should be hot,

yand upon the depth to which the surface pores Aare to be leached.

It is desirable to leach to such a depth that the concentration of soluble salts in the surface portion after subsequent drying will be no greater and preferably Will be less than. that in the interior of the glass. The latter condition produces after ring a compressional stress in the surface portion of the article, due to the lower thermal expansion coecient of the surface portion as compared to the interior. The differential stresses vmay readily be measured by optical methods vin the usual manner. I have found that the desired condition is attained at a temperature near the boiling point of the solution if the immersion time is one to two minutes for a glass thickness of about 1 mm. Longer times are required as the thickness is increased or the temperature of the solution is decreased.

In order that the invention may be better understood, reference is had to the accompanying drawing which illustrates a simple form of an apparatus for making tubular graded seals as one embodiment of the invention and in which Fig. lis a side view partly in section of an 'oven in which is disposed for heating a glass jar Fig. 2 is a sectional view of a glass jar lcontainl ing a'dilute vacid solution in which impregnated porous glass tubes are immersed for the purpose of leaching out some of the impregnating niaterial from the pores in the surface of the glass.

Fig. 3 is a side view partly in section of .a drying oven within which is a glass jar containing impregnated and leached porous glass tubes to be dried.

Fig. 4 is a sectional view of a tubular electric resistance furnace containing dried impregnated porous glass tubes to be preliminarily fired; and

Fig. 5 is a sectional view of a tubular furnace having zones of different temperatures separated by refractory insulation and containing in position for ring a porous glass tube one end of which has been impregnated.

In practicing the invention the porous glass articles, for example porous glass tubes to be converted to graded seals, are impregnated by immersing them for a portion of their length in a solution containing a soluble glass making material the oxide of which is to be incorporated therein as shown in Fig. 1. Preferably the solution is heated to increase the solubility of the material and to facilitate the impregnation. Suincient time should be allowed to permit the pores to become completely lled with the solution and fora tube having a wall thickness of about 1 mm. I have found that 2 hours is sufficient for complete impregnation.

The impregnated tubes are then immersed in a suitable solvent for the soluble glassrnaking material, preferably hot water acidulated with about 1% by Iweight of a strong acid to leach a ,for .a glass thicknessv of about 1 mm. when the solvent is maintained near its boiling point.

After a brief rinsing in cold water, the impregnated porous glass tubes are heated in air slowly The Vdried impregnated tubes are then transferred to -an electric resistance furnace in which they are heated for about nine or ten hours up to about 550 C., and for about two hours up to about 725 C., as shown in Fig. 4. This eliminates volatile substances from the pores and sinters the impregnated parts.

The tubes are nally transferred individually to a furnace with two temperature zones as shown in Fig. 5, in which the impregnated and unimpregnated portions are fired simultaneously. The impregnated portionis heated at about 9001000 C., and the unimpregnated portion is heated at about 1300-1350 C. At these temperatures consolidation *requires only about two minutes, but lower or higherv temperatures may be employed, if desired, with correspondingly different times. Alternatively, the impregnated and the unimpregnated ends may be fired individually.

Porous glasstubes having a length of about 4 inches, a diameter of about .5` inch and a Wall thickness of about l mm.' may be treated by the above described process using impregnating solutions having the compositions set forth in the following examples which illustrate but do not limit the invention:

` Example 1 H3BO3 grams 421 NazBiOfi (anhydrous) do 230 NHrOI-I (28% solution) cc-- 167 Water suicient to make 1 liter of solution.

Example .2

HaBOs grams 482 NazBiOv (anhydrous) do 178 K2CO31.5 H2O do 41 NHiOH (28% solution) cc-- 167 Water sufficient tomake 1 liter of solution.

Y Example 3 H3BO3 grams 8.3 KB5Os-4H2O do 667 Na2B4O7 (anhydrous) do 58.4 NHiOH (28% solution) cc 167 Sodium silicate solution (NazO-l-3.36 SiOz,

sp. gr. 1.395) cc 16.7 Water suicient to makel 1 liter of solution.

` Example 4 KB5O8-4H2O grams 667 K2B407'5H2O d0 83 LiNOa-Sl-IzO do 342 vNI-IiOH (28% solution) cc 167 Water sufficient to make 1 liter of solution.

A 'porous glass tube, one end of which has been impregnated with any one of the above described solutions followed by drying and firing the tube as described above, is suitable for use as a graded seal between fused silica or glass comprising over 94% SiOz and low expansion borosilicate glasses. The thermal expansion coefficients of the impregnated ends of such tubes when nished are in the neighborhood of .0000030 cm. per cm. per degree C. in the range of 7 to 300 C.

Other procedures for carrying out the various steps of the process will suggest themselves to those skilled in the art and different temperatures and times and solutions of different compositions from those set forth above may be employed within the scope oi the claims.

I claim:

1. The method of treating an article composed of a glass containing at least 94% SiOz and having intercommunicating pores throughout its mass, which com-prises impregnating at least a part of the article with a solution containing a compound of a glass-making oxide to substantially fill the pores therein, immersing the impregnated part in a solvent for the compound to remove part of the compound from the surface portion thereof, drying the article and firing it to close the pores and incorporate the oxide into the glass.

2. The method of treating an article composed of a glass containing at least 94% S102 and having intercommunicating pores throughout its mass, which comprises impregnating at least a part of the article with a solution containing a compound of a glass-making oxide to substantially fill the pores therein, immersing the impregnated part in an lacidic solvent for the compound to remove part of the compound from the surface portion thereof, drying the article and ring it to close the pores and incorporate the oxide into the glass.

3. The method of treating an article composed of a glass containing at least 94% SiOz and having intercommunicating pores throughout its mass, which comprises impregnating at least a part of the article with an alkaline solution containing a compound of a glass-making oxide to substantially lill the pores therein, immersing the impregnated part in an acidic solvent for the compound to remove part of the compound from the surface portion thereof, drying the article and ring it to close the pores and incorporate the oxide into the glass.

4. The method of treating an article composed of a glass containing at least 94% SiO2 and having intercommunicating pores throughout its mass, which comprises impregnating atv least a part of the article with an aqueous solu' tion containing a compound of boron oxide to substantially fill the pores therein, immersing the impregnated part in an acidic solvent for the compound to remove part of the compound from the surface portion thereof, drying the article and firing it to close the pores and incorporate the boron oxide into the glass.

5. The method of treating an article composed of a glass containing at least 94% SiOz land 'having intercommunicating pores throughout its mass, which comprises impregnating at least a part of the article with an aqueous solution `containing a compound of boron oxide and a compound of an alkali metal oxide to substantially ll the pores therein, immersing the impregnated part in an acidicsolvent for the compounds to remove part of thev compounds from the surface thereof, drying the article and firing it to close the pores and incorporate the boron oxide and alkali metal oxide into the glass.

6- The method according to claim 5 in which `the impregnating solution is an aqueous ammoniacal solution saturated with silica and containing a compound of boron oxide and a compound of an alkali metal oxide.

'7. The method according to claim 2 in which the acidic solvent is maintained at an elevated temperature.

8. The method according to claim 2 in which the acidic solvent is maintained at substantially its boiling point and the impregnated part is immersed in such solvent for l to 2 minutes per mm. of glass thickness.

9. The method according to claim 4 in which the impregnating solution is an aqueous ammoniacal solution containing a compound of boron oxide.

10. The method according to claim 4 in which the impregnated solution is an aqueous ammoniacal solution saturated with silica and containing a compound of boron oxide.

11. The method according to claim 5 in which the Iproportion of boron oXide is larger than the proportion of alkali metal oxide.

ROBERT V. LUKES.

REFERENCES CITED UNITED STATES PATENTS Name Date Dalton Dec. 7, 1943 Number 

1. THE METHOD OF TREATING AN ARTICLE COMPOSED OF A GLASS CONTAINING AT LEAST 94% SIO2 AND HAVING INTERCOMMUNICATING PORES THROUGHOUT ITS MASS, WHICH COMPRISES IMPREGNATING AT LEAST A PART OF THE ARTICLE WITH A SOLUTION CONTAINING A COMPOUND OF A GLASS-MAKING OXIDE TO SUBSTANTIALLY FILL THE PORES THEREIN, IMMERSING THE IMPREGNATED PART IN A SOLVENT FOR THE COMPOUND TO REMOVE PART OF THE COMPOUND FROM THE SURFACE PORTION THEREOF, DRYING THE ARTICLE AND FIRING IT TO CLOSE THE PORES AND INCORPORATE THE OXIDE INTO THE GLASS. 